Herein, we report the synthesis of [bis(hexamethylene)cyclopentadienone]iron tricarbonyl (1 b) by the reaction of cyclooctyne with Fe(CO)5 and the investigation of its catalytic properties in C=O bond reduction. As a result of the peculiar reactivity of cyclooctyne, 1 b was formed in good yield (56 %) by intermolecular cyclative carbonylation/complexation with Fe(CO)5. Compound 1 b was characterized fully and its crystal structure was determined by using XRD. Catalytic tests revealed that, upon in situ activation with Me3NO, 1 b promotes the hydrogenation of ketones, aldehydes, and activated esters as well as the transfer hydrogenation of ketones and shows a higher activity than the classical “Knölker complex” (1 a). Studies on the hydrogenation kinetics in the presence of 1 a and 1 b (respectively) suggest that this difference in activity is probably caused by the better stability of the 1 b‐derived complex than that of the in situ generated Knölker–Casey catalyst.

1H spin lattice relaxation rate (R 1) dispersions were acquired by field-cycling (FC) NMR relaxometry between 0.01 and 35 MHz over a wide temperature range on polyisoprene (IR), polybutadiene (BR), and poly­(styrene-co-butadiene) (SBR) rubbers, obtained by vulcanization under different conditions, and on the corresponding uncured elastomers. By exploiting the frequency–temperature superposition principle, χ″(ωτs) master curves were constructed by shifting the total FC NMR susceptibility, χ″(ω) = ωR 1(ω), curves along the frequency axis by the correlation times for glassy dynamics, τs. Longer τs values and, correspondingly, higher glass transition temperatures were determined for the sulfur-cured elastomers with respect to the uncured ones, which increased by increasing the cross-link density, whereas no significant changes were found for fragility. The contribution of polymer dynamics, χ pol ″(ω), to χ″(ω) was singled out by subtracting the contribution of glassy dynamics, χ glass ″(ω), well represented using a Cole–Davidson spectral density. For all elastomers, χ pol ″(ω) was found to represent a small fraction, on the order of 0.05–0.14, of the total χ″(ω), which did not show a significant dependence on cross-link density. In the investigated temperature and frequency ranges, polymer dynamics was found to encompass regimes I (Rouse dynamics) and II (constrained Rouse dynamics) of the tube reptation model for the uncured elastomers and only regime I for the vulcanized ones. This is clear evidence that chemical cross-links impose constraints on chain dynamics on a larger space and time scale than free Rouse modes.

In this paper, we describe a small library of easy-to-prepare chiral (cyclopentadienone)iron precatalysts for enantioselective C=O and C=N hydrogenations. Starting from readily accessible achiral materials, six chiral (cyclopentadienone)iron complexes (1a-f) possessing a stereogenic plane were synthesized in racemic form. Based on the screening of pre-catalysts (±)-1a-f in the hydrogenation of ketones and ketimines, we selected two complexes (1a and 1d) for resolution by semipreparative enantioselective HPLC. The absolute configuration of the separated enantiomers of 1a and 1d was assigned by XRD analysis (1a) and by comparison between experimental and DFT-calculated ECD and ORD spectra (1d). The enantiopure pre-catalysts (S)-1a and (R)-1d were tested in the asymmetric hydrogenation of several ketones and ketimines and showed good activity and modest enantioselectivity, the e.e. values ranging from very low to moderate (54%).

Here we report the catalytic transfer hydrogenation (CTH) of non-activated imines promoted by a Fe-catalyst in the absence of Lewis acid co-catalysts. Use of the (cyclopentadienone) iron complex 1, which is much more active than the classical 'Knö lker complex' 2, allowed to reduce a number of N-aryl and N-alkyl imines in very good yields using iPrOH as hydrogen source. The reaction proceeds with relatively low catalyst loading (0.5-2 mol%) and, remarkably, its scope includes also ketimines, whose reduction with a Fe-complex as the only catalyst has little precedents. Based on this methodology, we developed a one-pot CTH protocol for the reductive amination of aldehydes/ ketones, which provides access to secondary amines in high yield without the need to isolate imine intermediates.

Thanks to a highly active catalyst, the scope of the (cyclopentadienone)iron complex-promoted ‘hydrogen-borrowing’ (HB) amination has been expanded to secondary alcohols, which had previously been reported to react only in the presence of large amounts of co-catalysts. A range of cyclic and acyclic secondary alcohols were reacted with aromatic and aliphatic amines giving fair to excellent yields of the substitution products. The catalyst was also able to promote the cyclization of diols bearing a secondary alcohol group with primary amines to generate saturated N-heterocycles.